1. Field of the Invention
The present invention relates to a technique for performing electric connection from a light-emitting chip to a circuit board via an intermediate layer of a sub-mount in a light-emitting device that mounts a light-emitting chip by using a sub-mount.
2. Description of the Background Art
There is known a lamp unit including a lens and a reflector that uses a light-emitting device such as a light-emitting diode (LED) as a light source. For example, in application to a vehicular lighting fixture, it is possible to obtain desired light distribution using a direct projection-type or reflective-type unit.
FIGS. 7 and 8 schematically show examples of the structure of such a light-emitting device.
In the example a shown in FIG. 7, an LED chip (d) and an electrostatic protection element (such as a Zenor diode and a capacitor) (e) are mountedon conductor patters (c, c) formed on a circuit board (b) and the LED chip (d) and the electrostatic protection element (e) are covered by a lens body (not shown).
In this example, the range of a solid angle “α” that is formed around the light-emitting part of the LED chip (d) and shown by broken lines (f, g) and a double-headed arrow in FIG. 7 serves as a light application range. In other words, the light application range is narrowed by the influence of shielding of light caused by a component such as the electrostatic protection element (e).
As shown by (h) in FIG. 8, by arranging a sub-mount (i) on the circuit board (b) and mounting the LED chip (d) on its surface, it is possible to increase the light application efficiency.
The sub-mount (i) is bonded to the circuit board (b) via a bonding material. On the upper surface of the sub-mount (i) are formed conductor patterns (j, j) The LED chip (d) is mounted on the conductor patterns (j, j).
Electric connection between the conductor patterns (j, j) and conductor patterns (c, c) on the circuit board is made using gold wires (k, k).
The sub-mount (i) on which the LED chip (d) is mounted, the gold wires (k, k) and the electrostatic protection element (e) on the circuit board (b) are covered by a lens body (not shown).
In this example, the range of a solid angle “β” that is formed around the light-emitting part of the LED chip (d) and shown by broken lines (f′, g′) and a double-headed arrow in FIG. 8 serves as a light application range. In other words, it is possible to provide an ample light application range in the absence of the influence of shielding of light caused by a component such as the electrostatic protection element (e) (β>α).
The configuration of FIG. 8 has a problem that the gold wires for connecting the conductor patterns on the sub-mount and the circuit board shields the light emitted from the LED chip. That is, part of the gold wires (k, k) protruding above the upper surface of the sub-mount (i) (mounting surface of the LED chip (d)) results in a shadow of the part, thus influencing the light distribution.
The gold wire must be long enough to connect the conductor pattern (j) formed on the upper surface of the sub-mount (i) and the conductor pattern con the circuit board (b). For example, it is necessary to see to it that deformation resulting from stress caused by vibrations will not have an adverse effect on reliability. Additionally, gold wire has a very small diameter and thus a low strength, so that protection using a lens body is essential to protection from damage to the gold wire being handled.